<template>
  <ul class="list">
    <li class="item" v-for="item of letters" :key="item"
      @click="handleLetterClick"
      @touchstart="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      :ref="item"
    >{{item}}</li>
  </ul>
</template>

<script>
 export default {
  name: "CityAlphabet",
	props: {
		allCities: Object
	},
  computed: {
    letters () {
      const letters = []
      for (let i in this.allCities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop;
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if(this.touchStatus){
        if (this.timer) {
          clearTimeout(this.timer);
        }
        this.timer = setTimeout(() => {
          const startY = this.$refs["A"][0].offsetTop;
          const touchY = e.touches[0].clientY - 79;
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16);
        


      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
 }
</script>


<style lang="stylus" scoped >
  @import '~styles/varibles.styl'
  .list
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    display flex
    flex-direction column
    justify-content center
    .item
      text-align center
      line-height .4rem
      color $bgColor
</style>
